Ritualized behavior during competition for food between two formicinae

Summary Polyrhachis laboriosa andCamponotus brutus are two syntopic ants of the African equatorial forest. Although they occupy two different ecological niches (nesting area, diet, rhythms of activity), they are in competition for the exploitation of large permanent food sources. C. brutus, which is nocturnal, changed its rhythm of activity in the presence of large permanent food sources to exploit it day and night, whileP. laboriosa, diurnal, did not change its rhythm of activity. Encounters between workers of the two species at the food source always resulted in duels, even though several other workers were present. When attacked byC. brutus, P. laboriosa workers showed a novel flee-return strategy (fleeing over a 20-cm distance and returning to the source) instead of escaping definitively from the source and displayed ritualized behavior (i.e., fleeing, raising the gaster, flexing the gaster). These types of behavior appeasedC. brutus workers and enabledP. laboriosa to avoid overt aggression and to exploit the source in spite of the presence of a competitor. C. brutus also exhibited ritualized behavior during the duels (i.e., back-and-forth jerking of the body, series of light bites on a leg).C. brutus intimidatedP. laboriosa rather than really attacking it. This ritualization, used at an interspecific level, may be the result of a coevolutionary process or the effect of learning that certain types of behavior are beneficial. In any case, both species benefit from the possibility of exploiting large permanent food sources through confrontations that never lead to overt aggression.